ON THE PROPAGATION PRESSURE OF LONG CYLINDRICAL-SHELLS UNDER EXTERNAL-PRESSURE

Local imperfections induced in long tubes subjected to high external p ressures can lead to local collapse, from which a propagating buckle c an be initiated. This can result in catastrophic collapse of large sec tions of the structure. The propagation pressure is the lowest pressur e at which such a buckle will propagate. For common structural metal t ubes with diameter-to-thickness ratios of less than 100, the propagati on pressure is typically half an order of magnitude lower than the col lapse pressure of the intact tubes. As a result, the design of several tubular structures with external pressure loading requires that the c ollapse and propagation pressures be accurately known. This paper deal s with the experimental and analytical challenges of establishing the propagation pressure. A special purpose three-dimensional analysis, in combination with experimental observations and results, is used to de monstrate a mechanism of initiation of propagating buckles in long tub es, to study the parametric dependence of the propagation pressure and to illustrate the effect of axial tension on the propagation pressure . Propagation pressures predicted with this analysis are used to evalu ate the strengths and weaknesses of simpler models developed in the pa st.